Inherent storage for charged particle beam scanner

ABSTRACT

The output of an area of a charged particle source such as an electron source passes from this source through a plurality of control plates to a target which may comprise a phosphor target plate. The control plates have a plurality of apertures formed therein which are aligned with each other from plate to plate to define channels between the electron source and the target. The target is scanned by means of digital control signals which are applied to the control plates. A collector plate and a storage plate are interposed between the control plates and the phosphor target in that order. Control signals are successively applied to the various plates to first write signals onto the storage plate in accordance with the digital excitation of the control plates, to then apply the signals stored in the storage plate to the phosphor during a flood mode, and finally to erase the signals stored in the storage plate.

United States Patent Goede INHERENT STORAGE FOR CHARGED PARTICLE BEAMSCANNER Walter F. Goede, Harbor City, Calif.

Northrop Corporation, Los Angeles, Calif.

Sept. 9, 1971 Inventor:

Assignee:

Filed:

Appl. No.:

References Cited UNITED STATES PATENTS 10/1968 l-lultberg et a1 ..315/1212/1969 Novotny ..315/12 4/1970 Jeffries ..315/12 PrimaryExaminer-Leland A. Sebastian Attorney--W. M. Graham et al.

[5 7] ABSTRACT The output of an area of a charged particle source suchas an electron source passes from this source through a plurality ofcontrol plates to a target which may comprise a phosphor target plate.The control plates have a plurality of apertures formed therein whichare aligned with each other from plate to plate to define channelsbetween the electron source and the target. The target is scanned bymeans of digital control signals which are applied to the controlplates. A collector plate and a storage plate are interposed between thecontrol plates and the phosphor target in that order. Control signalsare successively applied to the various plates to first write signalsonto the storage plate in accordance with the digital excitation of thecontrol plates, to then apply the signals stored in the storage plate tothe phosphor during a flood mode, and finally to erase the signalsstored in the storage plate.

11 Claims, 7 Drawing Figures PATENTEDum a 1 m2 SHEET 1 BF 3 FIG. I

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WALTER F. GOEDE FIG.2

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WALTER F. GOEDE SOKOLSK I 8 \AOHLGEMUTH ATTORNEYS PATENTED our 3 I 1912SHEET 3 BF 3 FIG. 6

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WALTER F. GOEDE SCKOLSKI 8| WOHLGEMUTH ATTORNEYS INIIERENT STORAGE FORCHARGED PARTICLE BEAM SCANNER This invention relates to charged particlebeam scanners such as electron beam scanners, and more particularly to adigitally controlled scanner which utilizes storage in itsimplementation.

An electron beam scanning device which can be controlled in response todigital signals and which utilizes a plurality of flat control platessandwiched between an area cathode and a target is described in U.S.Pat. No. 3,539,719, my application Ser. No. 853,172 filed Aug. 26, 1969,now US. Pat. No. 3,600,627 and application Ser. No. 83,909 filed Oct.26, 1970, all of which are assigned to Northrop Corporation, theAssignee of the present application.

In the device described in the aforementioned U.S. Pat. No. 3,539,719and application Ser. No. 853,172, electron beam multiplication by meansof dynodes is utilized in order to provide sufficient electron beamcurrent to afford adequate brightness of the target image. The use ofelectron beam multiplication involves significant expense and adds tothe complexity of implementing the operation of the device in an optimumfashion. Also, for many application require ments, especially thoseinvolving high speed scanning, even with electron beam multiplicationthe brightness of the image is often less than would be desired.

The device of this invention affords a significant improvement in theoperation of digital electron beam scanners as described in theaforementioned patent and patent applications in providing an increasedbrightness in the display without the need for any multiplier plates.Further, it is possible to use lower switching rates in view of the factthat the dwell time per display element can be substantially increasedby virtue of storage. In addition, there is reduced power dissipation,and an overall increase in the efficiency of operation as a result ofthe storage implementation. In addition, the storage feature reduces oreliminates the requirement for frequent refreshing or rewriting ofinformation by the original source, usually a computer, digital memory,or direct sensor.

The use of storage in cathode ray tubes is well known in the art.However, these implementations have a number of distinct shortcomings.These include the requirement for an extra electron gun for effectingflooding, the need for a much larger envelope and a complex collimatingsystem. Further, an extremely tine screen mesh is required for adequateresolution in cathode ray tube implementations, which is expensive anddifficult to fabricate. Also, the resolution attainable with CRT storagetubes is somewhat limited, and the storage meshes tend to be ratherfragile, so that the device does not lend itself to operation in arugged environment.

The storage device of this invention, as implemented with an electronbeam scanner, has none of the above mentioned shortcomings. Noadditional electron source, complex collimating system, or significantlylarger envelope are required. As a matter of fact, the device of thisinvention can be added to an existing electron beam scanner of the typedescribed in the aforementioned patent at a rather nominal increase insize or cost. Thus, significant advantages are achieved with the storagedevice of the present invention in an electron beam scanner of the typedescribed in the aforementioned patent and patent applications, withoutany of the problems and shortcomings normally associated with this typeof device as implemented in the prior art in cathode ray tubestructures.

It is therefore an object of this invention to significantly improve thebrightness of the display in a digitally controlled charged particlebeam scanner of the type described.

It is a further object of this invention to improve the efficiency ofoperation of such an electron beam scanner.

It is still another object of this invention to provide a storage devicein an electron beam scanner display device which is relativelyeconomical and simple to fabricate.

It is still another object of this invention to provide an improvedelectron beam scanner device with inherent storage capability whichoperates in a highly efficient manner.

It is still another object of this invention to provide an improvedelectron beam scanner device having inherent storage capability in whichthe structure for such capability does not contribute significantly toincrease the size, complexity or cost of the device.

Other objects of this invention will become apparent as the descriptionproceeds in connection with the accompanying drawings, of which:

FIG. 1 is a schematic drawing illustrating the basic features of thedevice of the invention;

FIG. 2 is a graph illustrating the operation of the storage plate of theinvention;

FIG. 3 is a timing diagram illustrating the operation of the device ofthe invention in its various operation modes;

FIG. 4 is an elevational view in cross section illustrating oneembodiment of the device of the invention;

FIG. 5 is a cross sectional view in partial cutaway section taken alongthe plane indicated by 5-5 in FIG. 4;

FIG. 6 is a perspective view illustrating an alternative storage platewhich may be utilized in the device of the invention; and

FIG. 7 is a perspective view illustrating another alternative storageplate which may be utilized.

Briefly described, the device of the invention comprises an area chargedparticle source such as an electron source and a flat plate targetbetween which is sandwiched a plurality of control plates which haveapertures therein defining electron beam channels. It is to be notedthat while the device is described in connection with an electron beam,it may find application with other charged particle beams such as may beformed by positive or negative ions. The control plates may be digitallyexcited to control the flow of electrons through the channels formedtherethrough. interposed between the control plates and the target is astorage plate having a secondary emissive layer, which may be adielectric, deposited thereon. A collector plate, which is similar tothe scanning plate except that it has overall electrodes on both sidesrather than finger pattern electrodes, is located between the storageelectrode and the control electrode to provide a return path forsecondary electrons from the storage electrode. To increase contrast, acontrast enhancing plate may be placed between the storage electrode andthe target to increase the contrast of the display by acting as ablanking grid during the erase mode to prevent electrons from reachingthe target during this mode of operation.

In the operation of the device, three sequential operational modes areutilized: An erase, write, and flood mode. During the erase mode,potentials are applied to the various plates to place a uniform chargeover the entire area of the dielectric surface of the storage plate suchas to effectively erase any signals stored thereon. During the writemode, the control plates receive digital signals to control the electronbeam therethrough and simultaneously potentials are placed on theremaining plates to cause the scanning pattern to be stored on thestorage plate by appropriately charging the dielectric surface of thisplate.

, Finally, during the flood mode, the electrical charge informationstored on the storage plate is used to appropriately energize thetarget.

Referring now to FIG. 1, the device of the invention is schematicallyillustrated. Area cathode 11, which includes electron emitting filaments11a, provides a source of electrons over a scanning area defined byscanning control plates 12. Area cathode 11 may be of the type describedin the aforementioned patent application Ser. No. 83,909, while thescanning control plates 12 may operate in response to digital signals asdescribed in US. Pat. No. 3,539,719, and my application Ser. No. 853,l72now US. Pat. No. 3,600,627. In view of the brightness enhancement of thepresent invention it is not necessary that the control plates 12 beelectron multiplying dynodes, or that any type of electronmultiplication whatsoever be used. Interposed between scanning controlplates 12 and target 15, which may comprise a phosphorescent coating 15adeposited on a clear glass plate 15b, are collector plate 14 and storageplate 13. Storage plate 13 may comprise a backing plate portion 13a of aconductive metal such as nickel, having a thin layer 13b of dielectricsecondary emitting material such as magnesium fluoride or a base layerof calcium fluoride having magnesium oxide deposited thereover. As to beshown in connection with the specific embodiments of FIGS. 4-6, backingelectrode 13a may be a metal mesh having ll,000 lines/inch, may be athin metal plate having apertures formed therein to match the channelapertures of scanning control plates 12, or may be a dielectricsubstrate having a metallic coating. Plates l4 and 16 may both be metalplates having apertures formed therein which match and are aligned withthe channels defined by the control plate apertures. These plates mayalso be formed on a dielectric substrate, this substrate being metalclad on both of the broad surfaces thereof with interconnecting throughholes which also are metal coated to interconnect the electrodes on theopposite surfaces thereof such as described in application Ser. No.89,879 filed Nov. 16, 1970 and assigned to Northrop Corporation.

The dielectric coating 13b may be deposited by means of vacuumdeposition techniques to a thickness of the order of lmicrons. Thiscoating is on the surface facing the control plates and on the surfacesof the apertured portions. The thickness of deposition is dictated bythe particular application requirements at hand, a thicker layerproviding a lower capacitance with a faster write time capability. It isto be noted,

however, that too thick a layer may adversely affect other performancecharacteristics such as the storage capability.

Referring now to FIGS. 4 and 5, one embodiment of the device of theinvention is illustrated. The details of structure will be but brieflydescribed in view of the fact that they are thoroughly set forth in theaforementioned application Ser. No. 83,909 which is incorporated hereinby reference. Thermionic area cathode 11 is supported within evacuatedcasing 20. Supported in stacked relationship on insulating rods 35 arecontrol plates 12, which as already noted may be controlled in responseto digital signals. Mounted on insulating rods 35 between the controlplates 12 and phosphorescent target 15 are collector plate 14, storageplate 13 and contrast enhancement plate 16. If intensity modulation ofthe signal is desired, a modulation electrode providing the functions ofa control grid may be included, as described in US. Pat. No. 3,539,719.Storage plate 13 for this embodiment as can be seen in FIG. 5 is a wiremesh 13a with dielectric coating 13b deposited thereon.

Referring now to FIG. 6, an alternative configuration which may beutilized for the storage plate 13 is illustrated. This alternativestorage plate is fabricated of a metal plate 13a having apertures 13cformed over substantially the entire surface area thereof, theseapertures corresponding to and being aligned with the apertures formedin control plate 12. The plate has a dielectric secondary emissivecoating 13b deposited thereon.

Referring to FIG. 7, another form of storage plate which may be utilizedis illustrated. This plate comprises a dielectric substrate with anoverall conductive electrode 13d on one side thereof and secondaryemissive metallic coatings 13b forming collars in and around apertures13c on the side thereof towards the cathode.

Referring now to FIGS. 2 and 3, the operation of the device of theinvention will now be described. FIG. 3 illustrates typical operatingpotentials that have been successfully used in an operating embodimentof the device of the invention, but of course these can be variedsomewhat in other embodiments to achieve the desired results. FIG. 2illustrates a typical secondary emission curve which will be used todemonstrate the operation of the storage plate.

Referring first to FIG. 2, which is a plot of secondary emission ratioagainst primary electron beam energy, it can be seen that for allelectron beam energies between 0 and V the secondary emission ratio isless than unity and for all beam energies above this level, thesecondary emission ratio is greater than unity. This indicates that inthe region to the left of V the storage surface will be charged in anegative direction, while to the right of V the storage surface ischarged in a positive direction. The primary electron beam energy (theenergy of electrons striking the storage plate) can be determined by thevoltage applied to the backing electrode 13a of this plate.

The initial sequence in the operation of the device is to erase or primethe storage surface. This entails charging the storage dielectricmaterial negatively with respect to the backing electrode. Referring toFIG. 3, this is achieved in the following manner. To simplify therepresentation, the times for the various modes of operation are shownto be the same but in actual practice their lengths would differ fromeach other considerably. It is to be noted that in FIG. 3 the potentialsshown in the successive lines are those applied to the various plateswith respect to the potential of the area cathode as follows:

V R contrast enhancement plate V H backing electrode of storage plate Vtrace of storage elements of dielectric layer previously written and tobe re-written during cycle after erasure V trace of storage elementswhich have not been written V collector plate The line designated Vrepresents the modes of operation of scanning control plates 12 and doesnot represent potentials applied.

The contrast enhancement plate is placed at a voltage (V which is belowthe cathode potential Volts). This prevents electrons which will be usedto erase the storage plate from reaching the target during the erasingoperation. While the use of this contrast enhancement plate is notabsolutely necessary to make for an operative device, it significantlyincreases the contrast of the displayed image by preventing the targetfrom brightening in response to the electrons used for erasing, whichcould otherwise pass through during the erase cycle. This of coursewould give an overall average brightness background which would resultin reduced contrast.

The backing electrode 13a of the storage plate is simultaneously placedat a potential (V which is below the cross-over potential (V shown anddescribed in connection with FIG. 2. For the illustrative example, thiswas approximately 25 Volts above cathode potential.

The scanning control plates 12 are all placed in an on" state or floodmode such that all the channels are forward biased by the application ofthe appropriate potentials (approximately 100 volts). The net result ofthis is that flood electrons from the area cathode collide with thestorage dielectric. Since the electrons striking the dielectric have anenergy below V the dielectric material is charged negative with respectto the backing electrode. Thus, for storage elements which hadpreviously been written, the voltage on the dielectric element goes tozero (cathode potential) as indicated by V which is about 30 voltsnegative charge with respect to the backing electrode. For unwrittenstorage elements, of course, as shown by the trace V the voltage on thedielectric element remains at approximately zero (cathode potential)throughout the erase mode, this being a 30 volt negative charge withrespect to the backing electrode. It is to be noted that in theoperative embodiment of the invention referred to, less than 100microseconds is required for total screen erasure.

Following the erase mode, the write mode occurs, during whichinformation is written on the storage dielectric of the storage plate.During this mode, the scanning control plates are operated in their scanmode during which they are appropriately activated in response todigital control signals in the manner described in the aforementionedUS. Pat. No. 3,539,719. The backing electrode of the storage plate iselevated to a potential (V greater than V (of the order of severalhundred volts), such that the secondary emission ratio is greater thanone. Simultaneously, the collector electrode is placed at a potential (Vsomewhat higher than that on the backing electrode, to collect secondaryelectrons generated at the dielectric surface. The contrast enhancementplate is also elevated to a potential (V above the backing electrode.This allows some of the writing electrons to pass through to thephosphor target. A full frame of information is now written onto thestorage target. In FIG. 3, for illustrative purposes, V illustrates thecharging of a storage element opposite the channel in which informationis being written, while V indicates the charge on a storage elementopposite a channel which is cut off. It is to be noted that in theoperative embodiment of the subject invention, less than 0.5microseconds is required to write a single element.

The next and final mode of operation is the flood mode. In this mode,the electrical charge information that was written onto the storageplate is used to present a visual output on the phosphor target. Apotential V is first applied to the electron beam scanning plates toplace them in the flood mode as previously described in connection withthe erase mode. Simultaneously, the collector plate is brought to apotential V (approximately 50 volts), and the backing electrode of thestorage plate is brought to a potential V near cathode potential(approximately 20 volts), such that areas V of the dielectric layerwhich were charged positively during the write mode will transmit floodelectrons, and areas V which were charged negative during the erase modeand left undisturbed in the write mode, will repel the incoming floodelectrons. The repelled electrons are collected at the collector plate.The contrast enhancement plate is placed at a voltage V above that ofthe backing electrode, such that the flood electrons coming through thestorage plate will be refocused and directed onto the target. The threemodes of the cycle are thus completed and a new similar cycle commenced.

The device of this invention thus provides simple and economical meansfor significantly increasing the brightness of the display of adigitally controlled electron beam scanner. This end result is achievedwithout addition of appreciable structures to an existing device andwithout greatly increasing the cost thereof. Inherent memory is alsoadded to the device, eliminating, in some cases, the need for a refreshmemory in the electronics.

Iclaim:

1. In a charged particle beam scanner having an area cathode, a targetfor receiving electrons from the cathode and control plate means havingapertures therein defining beam channels running from the cathode to thetarget for controlling the flow of charged particles in said channels,the improvement comprising:

storage plate means interposed between the control plate means forstoring charge in accordance with the charged particle flow through saidchannels during a first mode of operation and releasing chargedparticles to the target during a second mode of operation, and

collector plate means interposed between the control plate means andsaid storage plate means and having apertures aligned with said channelsfor providing a return path for charged particles from said storageplate means,

a first set of potentials being applied to said storage and said controlplate means during said first mode to bring the secondary chargedparticle yield of said storage plate means to less than unity, a secondset of potentials being applied to said storage and said control meansduring said second mode to bring the secondary charged particle yield ofsaid storage plate means to above unity, and a third set of potentialsbeing applied to said storage and said control plate means during asubsequent mode of operation to erase the charge stored on said storageplate means.

2. The scanner of claim 1 wherein said storage plate means comprises aconductive wire mesh having a dielectric secondary emissive materialdeposited on the surface thereof facing said control plate means.

3. The scanner of claim 1 wherein said storage plate means comprises aflat conductive plate having apertures aligned with said channels formedtherein, a dielectric secondary emissive material being deposited in theapertured portions of said plate and on the surface thereof facing saidcontrol plate means.

4. The scanner of claim 1 wherein said storage plate means comprises aflat dielectric plate having apertures aligned with said channels formedtherein, a secondary emissive material being deposited in the aperturedportions of said plate on at least a portion of the surface thereofsurrounding said apertured portions and facing said control plate means,the opposite surface of said plate having a conductive material thereon.

5. The scanner of claim 1 and further including conductive plate meansinterposed between the storage plate means and the target for enhancingthe contrast of the target signal by preventing charged particles fromreaching the target during the erase mode.

6. An electron beam scanner comprising:

a flat area cathode;

a flat target for receiving electrons from said cathode;

a plurality of flat control plates sandwiched between the cathode andtarget for controlling the electron flow therebetween, said controlplates having apertures formed therein, the apertures on successivecontrol plates being aligned with each other to define electron beamchannels running between the cathode and target;

flat storage plate means sandwiched between the control plates and thetarget for storing charge thereon in accordance with the electron flowin said channels during a write mode of operation, the stored chargebeing used to energize said target during a subsequent flood mode ofoperation and being erased from said storage plate during a stillsubsequent erase mode of operation; and

collector plate means sandwiched between said storage plate means andsaid control plates for providing a return path for electrons from saidstorage plate means.

7. The scanner of claim 6 wherein said control plates have fingerpattern electrodes thereon for digitally controlligg the electron flow.

8. e scanner of claim 6 wherein said storage plate means comprises awire mesh having secondary emissive dielectric material depositedthereon.

9. The scanner of claim 6 wherein said storage plate means comprises aflat conductive backing plate having apertures formed therein alignedwith said channels, secondary emissive dielectric material beingdeposited on the surface of said plate facing said control plates and inthe apertured portions thereof.

10. The scanner of claim 6 wherein said storage plate means comprises aflat dielectric backing plate having apertures formed therein alignedwith said channels, secondary emissive material being deposited on theportions of the plate surface surrounding said apertures and facing saidcontrol plates and in the apertured portions thereof, the oppositesurface of said plate having a conductive material thereon.

11. The scanner of claim 6 wherein is further included conductive platemeans for enhancing the contrast of the target signal by preventingelectrons from reaching the target during the erase mode, saidconductive plate means having apertures aligned with said channelsformed therein.

1. In a charged particle beam scanner having an area cathode, a targetfor receiving electrons from the cathode and control plate means havingapertures therein defining beam channels running from the cathode to thetarget for controlling the flow of charged particles in said channels,the improvement comprising: storage plate means interposed between thecontrol plate means for storing charge in accordance with the chargedparticle flow through said channels during a first mode of operation andreleasing charged particles to the target during a second mode ofoperation, and collector plate means interposed between the controlplate means and said storage plate means and having apertures alignedwith said channels for providing a return path for charged particlesfrom said storage plate means, a first set of potentials being appliedto said storage and said control plate means during said first mode tobring the secondary charged particle yield of said storage plate meansto less than unity, a second set of potentials being applied to saidstorage and said control means during said second mode to bring thesecondary charged particle yield of said storage plate means to aboveunity, and a third set of potentials being applied to said storage andsaid control plate means during a subsequent mode of operation to erasethe charge stored on said storage plate means.
 2. The scanner of claim 1wherein said storage plate means comprises a conductive wire mesh havinga dielectric secondary emissive material deposited on the surfacethereof facing said control plate means.
 3. The scanner of claim 1wherein said storage plate means comprises a flat conductive platehaving apertures aligned with said channels formed therein, a dielectricsecondary emissive material being deposited in the apertured portions ofsaid plate and on the surface thereof facing said control plate means.4. The scanner of claim 1 wherein said storage plate means comprises aflat dielectric plate having apertures aligned with said channels formedtherein, a secondary emissive material being deposited in the aperturedportions of said plate on at least a portion of the surface thereofsurrounding said apertured portions and facing said control plate means,the opposite surface of said plate having a conductive material thereon.5. The scanner of claim 1 and further including conductive plate meansinterposed between the storage plate means and the target for enhancingthe contrast of the target signal by preventing charged particles fromreaching the target during the erase mode.
 6. An electron beam scannercomprising: a flat area cathode; a flat target for receiving electronsfrom said cathode; a plurality of flat controL plates sandwiched betweenthe cathode and target for controlling the electron flow therebetween,said control plates having apertures formed therein, the apertures onsuccessive control plates being aligned with each other to defineelectron beam channels running between the cathode and target; flatstorage plate means sandwiched between the control plates and the targetfor storing charge thereon in accordance with the electron flow in saidchannels during a write mode of operation, the stored charge being usedto energize said target during a subsequent flood mode of operation andbeing erased from said storage plate during a still subsequent erasemode of operation; and collector plate means sandwiched between saidstorage plate means and said control plates for providing a return pathfor electrons from said storage plate means.
 7. The scanner of claim 6wherein said control plates have finger pattern electrodes thereon fordigitally controlling the electron flow.
 8. The scanner of claim 6wherein said storage plate means comprises a wire mesh having secondaryemissive dielectric material deposited thereon.
 9. The scanner of claim6 wherein said storage plate means comprises a flat conductive backingplate having apertures formed therein aligned with said channels,secondary emissive dielectric material being deposited on the surface ofsaid plate facing said control plates and in the apertured portionsthereof.
 10. The scanner of claim 6 wherein said storage plate meanscomprises a flat dielectric backing plate having apertures formedtherein aligned with said channels, secondary emissive material beingdeposited on the portions of the plate surface surrounding saidapertures and facing said control plates and in the apertured portionsthereof, the opposite surface of said plate having a conductive materialthereon.
 11. The scanner of claim 6 wherein is further includedconductive plate means for enhancing the contrast of the target signalby preventing electrons from reaching the target during the erase mode,said conductive plate means having apertures aligned with said channelsformed therein.